The aerodynamic designs of winged drones are optimized for specific flight regimes. Large lifting surfaces provide maneuverability and agility but result in larger power consumption, and thus lower range, when flying fast compared with small lifting surfaces. Birds like the northern goshawk meet these opposing aerodynamic requirements of aggressive flight in dense forests and fast cruising in the open terrain by adapting wing and tail areas. Here, we show that this morphing strategy and the synergy of the two morphing surfaces can notably improve the agility, maneuverability, stability, flight speed range, and required power of a drone in different flight regimes by means of an avian-inspired drone. We characterize the drone’s flight capabilities for different morphing configurations in wind tunnel tests, optimization studies, and outdoor flight tests. These results shed light on the avian use of wings and tails and offer an alternative design principle for drones with adaptive flight capabilities.
Vertebrates, including amphibians, reptiles, birds, and mammals, with their ability to change the stiffness of the spine to increase load-bearing capability or flexibility, have inspired roboticists to develop artificial variable-stiffness spines. However, unlike their natural counterparts, current robotic spine systems do not display robustness or cannot adjust their stiffness according to their task. In this paper, we describe a novel variable-stiffness tensegrity spine, which uses an active mechanism to add or remove a ball-joint constrain among the vertebrae, allowing transition among different stiffness modes: soft mode, global stiff mode, and directional stiff mode. We validate the variable-stiffness properties of the tensegrity spine in experimental bending tests and compare results to a model. Finally, we demonstrate the tensegrity spine system as a continuous variable-stiffness manipulator and highlight its advantages over current systems.
Flight in dense environments, such as forests and cities requires drones to perform sharp turns. Although fixed-wing drones are aerodynamically and energetically more efficient than multicopters, they require a comparatively larger area to turn and thus are not suitable for fast flight in confined spaces. To improve the turning performance of winged drones, here we propose to adopt an avian-inspired strategy of wing folding and pitching combined with a folding and deflecting tail. We experiment in wind tunnel and flight tests how such morphing capabilities increase the roll rate and decrease the turn radius - two measures used for assessing turn performance. Our results indicate that asymmetric wing pitching outperforms asymmetric folding when rolling during cruise flight. Furthermore, the ability to symmetrically morph the wing and tail increases the lift force, which notably decreases the turn radius. These findings pave the way for a new generation of drones that use bird-like morphing strategies combined with a conventional propeller-driven thrust to enable aerodynamic efficient and agile flight in open and confined spaces.
There is a growing interest in unmanned aerial vehicles (UAVs) grasping, perching, and interacting with their surroundings by means of claws, arms, hooks, and other appendages. While multirotor vehicles can slowly lower onto a target object and grasp it, winged UAVs require a minimum speed to remain airborne and cannot hover. In this article, we describe a novel avian-inspired grasping mechanism that allows winged UAVs to grasp an object while flying over it. We have developed a high-speed, passively triggered claw that can close in under half a second. We characterize the loads encountered by the vehicle during the grasp event and find that grasping an object of about 30 g produces a maximum load of less than 12 N. Numerical experiments indicate that these loads cause a change in pitch of less than 1 • and a decrease in speed of about 0.3 m/s for a fixed-wing vehicle of about 1 kg, and are thus negligible. We demonstrate outdoor in-flight grasping at 8 m/s, the fastest recorded grasping by a flying robot to date to best of our knowledge.
Avian flapping strategies have the potential to revolutionize future drones as they may considerably improve agility, increase slow speed flight capability, and extend the aerodynamic performance. The study of live birds is time‐consuming, laborious, and, more importantly, limited to the flapping motion adopted by the animal. The latter makes systematic studies of alternative flapping strategies impossible, limiting our ability to test why birds select specific kinematics among infinite alternatives. Herein, a biohybrid robotic wing is described, partly built from real feathers, with more advanced kinematic capabilities than previous robotic wings and similar to those of a real bird. In a first case study, the robotic wing is used to systematically study the aerodynamic consequences of different upstroke kinematic strategies at different flight speeds and stroke plane angles. The results indicate that wing folding during upstroke not only favors thrust production, as expected, but also reduces force‐specific aerodynamic power, indicating a strong selection pressure on protobirds to evolve upstroke wing folding. It is also shown that thrust requirements likely dictate the wing's stroke tilting. Overall, the proposed biohybrid robotic flapper can be used to answer many open questions about avian flapping flights that are impossible to address by observing free‐flying birds.
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